1. Field of the Invention
The invention concerns the area of asynchronous networks with random transmission times, and more particularly multimedia communications linking together audio communication terminals of the LAN (Local Area Network) type, and video communication terminals, also of the LAN type, within such networks.
2. Description of the Related Art
By “audio communication terminal” is meant here any communicating network equipment capable of exchanging audio data, such as a fixed or mobile telephone for example, or a personal digital assistant (PDA). Likewise, by “video communication terminal” is meant here any communicating network equipment capable of exchanging video data, such as an individual computer for example.
In asynchronous networks with random transmission times, when, for example, two people, having activated a communication between their first* audio or video LAN communication terminals via a local area network (LAN) and a communication network, decide during the communication to communicate packets of audio or video data to each other, via second* audio or video LAN terminals respectively, independently of the first* terminals used, offset timing usually occurs between the packets of audio data and the packets of video data coming from a given user. More precisely, the audio packets generally arrive before the video packets, representing a nuisance for the user receiving the data.
This offset timing results mainly from the “non-deterministic” character of the transmission of data packets within asynchronous packet-switched networks, such as IP protocol networks for example. By “non-deterministic” is meant here the fact of being of a variable character which is not controllable over time (i.e. of a random nature). In fact, the streams of audio data packets and the streams of video data packets, due to their different natures, generally do not follow the same routes within the network and generally do not have identical priority levels. In addition, the routes taken even by data packets of the same type can vary.
But the offset timing results also from differences in the coding/decoding times of the video and audio data.
In order to attempt to improve the situation, it has been proposed that all of the audio streams should be delayed, in an automatic manner and by a constant value, in relation to the video streams. However, this constant delay enables one to overcome only the non-random transmission-time differences, such as those introduced by the coding/decoding operations, and these are not the most detrimental ones.